During conventional surgical procedures, a surgeon may use a patient's own tissue to repair or replace anatomical structures. These structures may be used with minimal modifications, such as when the saphenous vein is harvested from the leg and used as a conduit to supply blood flow to a coronary artery in cardiac bypass surgery. In other cases, the tissue can be significantly modified, and then used. The pericardium (the membranous sac around the heart) has been harvested, chemically treated, and then reconfigured to make heart valve leaflets for valve repair or replacement.
Constructing three-dimensional biological structures (“bio-structures”) in the operating room is difficult. Surgeons can't spend too long making complex functional structures from an individual's tissues, and there are limited tools available. The patient's tissues are limited in quantity, difficult to work with, and often not accessible or permissible to remove. These constraints restrict the sophistication of the current surgical procedures which involve manipulating a patient's own tissues (“autologous tissues”) during surgery. These limitations inhibit the clinician from envisioning new potential therapies and surgical strategies based upon complex modification of tissues in the operating room.
Prior strategies to overcome these difficulties include 1) pre-forming complex anatomical structures from synthetic materials prior to the surgery, 2) using non-synthetic tissues with inherent structure harvested from a range of sources, and 3) using specialized instrumentation for constructing complex biological structures in the operating room.
Textile technology has been used in medicine providing synthetic implants for patients. Weaves, knits, braids, and meshes of synthetic materials have been used in strips, sheets, and tubular configurations. As examples, woven or knitted polyester sewing rings are used in prosthetic heart valves and woven “Surgicel”™ cellulose or “Iodoform”™ gauze in sheets or strips are used for epitaxis and wound packing. Other examples include knitted Dacron (polyester) tubular conduits used in peripheral vascular surgery and braided stainless steel “Wallstent”™ cylinders for stenting the respiratory and gastrointestinal tract. Knitted polypropylene mesh sheets have found application to reduce tension in hernia repair. In these examples, textile processing is used to impose structure and promote tissue encapsulation of the synthetic (heart valve ring), trap cells to enhance blood clotting or absorb fluids (Surgicel or Iodoform), provide a three-dimensional configuration for fluid flow or stenting (vascular graft or Wallstent), or alter biomechanics, e.g. tensile strength or elasticity (hernia mesh).
In general, the application of textile technology (e.g. weaving, knitting, braiding) to a base material increases the implant's surface area, enlarges the interspaces between fibers, and increases the mass of material in the structure. In using synthetics as a base material, this processing also increases the mass of the foreign body which in many applications, imposes an increase risk of infection and immunological incompatibility. In addition, these structures are not living tissues and have no ability to repair, regenerate, or grow at the cellular, tissue or organ level.
Another strategy has been to use tissues from various sources to form the desiredbio-structures in patients. In certain instances, using tissues as a base material for implants imparts intrinsic three-dimensional structure, reduces the foreign body reaction, or retains the tissues living capabilities of cellular repair, regeneration, and growth. Tissue implants fall into three broad categories which include xenografts (from another species), homografts (from the same species), and autografts (from the same individual). Examples are glutaldehyde-fixed porcine pericardium heart valves (xenograft), kidney transplant from a cadaver (homograft), and skin grafts in burn patients (autograft). The general characteristics of xenografts, homografts, and autografts have unique properties as compared to native tissue. In general, tissue derived from a xenograft is less pliable and supple and incapable of cellular repair, regeneration, or growth characteristics since they are rendered nonviable due to chemical treatments used to reduce their immunogenicity. Homografts have more pliability than xenografts, but are non-living and scare in availability. Autologous tissues retain pliability and living capabilities but require careful non-traumatic handling and time-sensitive harvesting, reconstruction, and implantation to preserve these characteristics. The majority of xenografts, homografts, and autografts tissues have been used as implants without the application of textile technology to form the desired structures.
For the most part, surgeons rely on conventional hand-held surgical instrumentations for reconstructing tissues by incising, shaping, and suturing tissues into three-dimensional shapes. An example of the use of more specialized instrumentation is a split-thickness skin grafting technique during which the surgeon uses a dermatome to harvest a thin layer of patient's skin and a specialized slitting tool to make an array of incisions in the skin, allowing the graft to be expand into a mesh configuration with a larger surface area. Another prior use of intra-op instrumentation designed to create a three-dimensional shape is the use of specialized tissue cutting templates, jigs, and forms to create tri-leaflet heart valves from a planar sheet of the patient's pericardium. There are few examples of these tools for specialized procedures and they are not widely applied in surgery. The majority of surgery is performed using a standard set of hand-held instruments.